This invention relates in general to the manufacture of low pressure arc discharge lamps, and more particularly to a method of manufacturing the envelope of a compact fluorescent lamp having an increased voltage drop thereacross.
It is often desirable to substantially increase the voltage drop in a low pressure mercury discharge lamp without decreasing the efficiency of the discharge in producing UV radiation. This is especially true when it is desirable to keep the arc length of the lamp as short as possible and consequently minimize the overall physical dimensions of the lamp while maintaining the same light output. This is especially important in the case of compact fluorescent lamps.
It is known in the art that the voltage across an arc discharge lamp can be increased to obtain more radiation by varying the operating parameters of the discharge lamp, such as the lamp current loading, pressure, etc. However, altering these parameters affects the performance or some other aspect of the discharge lamp. It is known that increasing the lamp power by increasing the lamp current loading will result in more radiation in a given lamp length. Increasing the lamp power to more than a given value results in a decrease in the conversion efficiency of the electrical energy supplied to the lamp into useful radiation. Also, the circuit losses in the stabilizing choke increase with the increased lamp current.
Fluorescent lamps have been made in the past which attempt to increase the voltage drop across the lamp by means of indentations or grooves in the envelope. Examples of such lamps having a plurality of individual indentations formed in a periodic manner along the envelope to increase the effective arc stream length are shown in U.S. Pat. Nos. 2,916,645; 2,973,447; and 3,098,945. These configurated lamps which have elongated tubular envelopes with non-circular cross-sections are generally complicated and consequently rather expensive to manufacture.
Another lamp is shown in U.S. Pat. No. 3,988,633 in which a plurality of separate and continuous grooves are used to increase the radiation of the lamp by altering the wall recombination rate of the plasma ions with the phosphor. The additional voltage generated in this type of lamp is not substantial i.e., less than 1 volt per inch of arc length.